Mounting output from the Organization of the Petroleum Exporting Countries (OPEC) and its allies and lofty global natural gas prices are widening the spread between sweet and sour crude prices, the U.S. Energy Information Administration (EIA) said Friday.

crude prices

While crude prices have recently come off 2021 highs in large part because of coronavirus resurgence concerns, they remain firmly in positive territory for the year. However, prices of high-sulfur oils have been declining relative to low-sulfur alternatives, EIA said.

The alliance — known as  OPEC-plus — produces mostly medium- or high-sulfur oils, aka sour crude. Its mounting exports contributed to the expanding gulf. Sour oils typically sell at a discount to low-sulfur, or sweet, crude because they must first be treated with...